The present invention relates to a fuel pump for primary use with an automobile.
FIGS. 16 and 17 show one example of such a fuel pump in the related art, and FIGS. 18 and 19 show another example of the related art fuel pump.
Referring first to FIGS. 16 and 17 which are a vertical sectional view and a top plan view of the first example of the related art fuel pump, reference numeral 2 generally designates a fuel pump comprising a housing 4, a motor section 6 provided in the housing 4, and a pump section 8 provided at a lower portion of the housing 4.
The motor section 6 is constructed of a brushless motor 10 coaxially installed in the housing 4. The brushless motor 10 includes a fixed type armature 12 and a rotor magnet 14. The armature 12 is fixed to the housing 4, and it comprises a core 13 formed by stacking a plurality of stator plates and a coil 15 wound around the core 13. A motor shaft 18 is mounted through a collar 16 to the rotor magnet 14. A timing rotor 20 formed of a non-magnetic material is engaged with an upper surface of the rotor magnet 14, and a rotor cover 22 formed of a non-magnetic material is engaged with a lower surface of the rotor magnet 14. Thus, the assembly of the timing rotor 20, the rotor cover 22 and the rotor magnet 14 is fixedly mounted on the motor shaft 18. The motor shaft 18 is rotatably supported at its upper portion through the timing rotor 20, a timing rotor bearing 24 and a case holder 26 to the housing 4, while being rotatably supported at its lower portion through a motor shaft bearing 28 and a pump cover 30 forming a component of the pump section 8 to the housing 4.
The pump section 8 includes a pair of impellers 32 and 34 mounted on a lower end portion of the motor shaft 18. The impellers 32 and 34 are located in a space defined by the pump cover 30, a pair of annular spacers 36, a center plate 38 and a housing body 40, so that a pair of sectionally C-shaped pump chambers 42 and 44 are defined around the outer peripheries of the impellers 32 and 34, respectively. The pump chambers 42 and 44 are communicated with each other. The lower pump chamber 42 is communicated through a fuel inlet 46 formed through the housing body 40 to a fuel tank (not shown), while the upper pump chamber 44 is communicated through an outlet port (not shown) to the inside area of the housing 4.
In operation, when the motor section 6 is operated to rotate the impellers 32 and 34, fuel is sucked from the fuel inlet 46 into the pump chambers 42 and 44. The fuel sucked into the pump chambers 42 and 44 is pumped up through the outlet port into the housing 4. Then, the fuel is fed through an annular fuel passage defined between the armature 12 and the rotor magnet 14 to a fuel outlet 48 formed at an upper end of the fuel pump 2.
Referring next to FIGS. 18 and 19 which are a vertical sectional view and a top plan view of the second example of the related art fuel pump, the fuel pump has the same construction as that of the first example shown in FIGS. 16 and 17 except the construction of the motor section 6, the same reference numerals designate the same or corresponding parts, and accordingly the following description will be directed to the motor section 6 only.
The motor section 6 is constructed of a brush motor 110 coaxially installed in the housing 4. The motor 110 includes a rotary type armature 112 and a magnet 114 fixed to the housing 4. The armature 112 comprises a core 113 formed by stacking a plurality of plates and a coil 115 wound around the core 113. The motor shaft 18 is mounted at a central portion of the armature 112. A commutator 116 is mounted on an upper portion of the motor shaft 18, and it slidably contacts a brush 120 mounted through a brush holder 118 to the housing 4. The motor shaft 18 is rotatably supported at its upper end portion through a bearing 122 and a cover 124 to the housing 4, while being supported at its lower end portion through the motor shaft bearing 28 and the pump cover 30 to the housing 4.
As the prior art of the present invention, there are disclosed in Japanese Utility Model Laid-open Publication No. 61-96758 and Japanese Patent Publication No. 35-17264 a brush motor having an armature entirely covered with an adhesive layer having a substantially circular cross section.
In the above-mentioned related art as shown in FIGS. 16 to 19, there is a problem of noise due to vibration. Specifically, in the related art as shown in FIGS. 16 and 17, a high-frequency wave near 1 kHz is generated due to a fluctuation in electromagnetic force generated in the armature, and causes the vibration of the armature itself. The vibration of the armature is transmitted to the housing, causing vibration of the housing to generate the noise. A frequency (f) of the noise to be generated due to the fluctuation of the electromagnetic force is expressed as follows:
f=(rotating speed (r.p.m.) of the rotor magnet) x (the number of times of excitation of the coil per revolution of the rotor magnet).times.N/60 (where N is integer.) PA1 f'=(rotating speed (r.p.m.) of the armature).times.(the number of segments of the commutator).times.N/60 PA1 (where N is integer.)
On the other hand, in the related art as shown in FIGS. 18 and 19, the vibration of the armature is generated due to the sliding contact between the brush and the commutator or due to the same cause as mentioned above. A frequency (f') of the noise to be generated due to the sliding contact between the brush and the commutator is expressed as follows: